The present application is based on Japanese Patent Application No. Hei. 10-94899, which is incorporated herein by reference.
1. Field of the Invention
This invention relates to a coupling mechanism structured to connect a resin fuel hose with a metal pipe, and more particularly to a coupling mechanism including a resin coupling body having a pipe inserting section configured to permit the metal pipe to be inserted thereinto which is designed so that an O-ring can be fitted in an inner wall of the pipe inserting section of the coupling body.
In this specification, the term xe2x80x9celectrical deterioration of resinxe2x80x9d means that current flows in the contact part of different types of members, so that the resin is deteriorated. An electrical deterioration of the resin may include electrolytic deterioration and thermal (Joule heat) deterioration.
2. Description of Related Art
Japanese Patent Publication No. Hei. 4224394 presents general technical material to this topic level and is herein incorporated by reference.
A resin fuel hose generally requires a compound having characteristics such as resistance to gasoline and gasohol, and gasoline and moisture permeability resistance. Therefore, generally, a hose body 12 is of a multi-layer structure as shown in FIG. 1.
For instance, the resin fuel hose is designed as follows: A body layer 14 is formed of polyamide such as nylon, or the like, having excellent gasohol and moisture permeability resistance, and excellent flexibility. An inner layer (the innermost layer) 16 of fluoro-resin material has much higher gasoline resistance and gasoline permeability resistance than the nylon inside the body layer 14. See, for example, U.S. Pat. No. 5,383,087.
The inner surface of the resin fuel hose may become electrostatically charged by the flow of fuel. Therefore, it is necessary that the amount of electrostatic charge is suppressed to a predetermined value in order to prevent the occurrence of electrostatic trouble.
In order to discharge the static electricity (charge), the quick connector is generally made of a resin which has a volume resistivity lower than 106xcexa9xc2x7cm or a surface resistivity lower than 106 xcexa9. If the elctrically conductive quick connector is made of resin, for example, it can be more easily manufactured ( injection molding can be utilized) and will have a reduced weight.
It has been found, however, that the resin quick connector having the above-described electrical resistance also electrically deteriorates more rapidly.
In view of the foregoing, an object of the invention is to provide a fuel hose resin coupling in which the coupling body has a slow electric deterioration.
The inventors have conducted intensive research on the solution of the above-described problem, and found that the cause for the electrical deterioration of the resin coupling is as follows:
In the discharge path (or charge leak path) of the inner layer 16, the coupling body 24, and the metal pipe 22, a gap which is for the assembling of the metal pipe 22 and the coupling mechanism 18 is provided between the metal pipe 22 and the pipe inserting section 26 of the coupling body 24. The gap between the metal pipe 22 and the pipe inserting section 26 is sealed with O-rings 28. Because of the function of the O-ring 28, its electrical resistance is high enough to prevent the leakage of static electricity. In order to lower the electrical resistance, a large quantity of carbon black is employed to reduce the electrical resistance of the O-ring. However, in order to seal the gap well, it is not suitable to employ a large quantity of carbon black.
Therefore, moving the charge from the inner layer 16 to the coupling body 24 occurs as follows: when the metal pipe 22 is brought into point-contact with the coupling body 24 because of the vibration of the traveling vehicle, current in the form of static electricity flows in the inner layer 16, in the contact part of the coupling body 24 and the metal pipe 22. This current is a factor which expedites the deterioration (or dissolution) of the resin coupling body 24 of resin.
That is, the static electricity generated in the inner layer 16 is removed through a nipple 20 of coupling mechanism 18 and through the metal pipe 22 which is connected to the coupling mechanism 18 and grounded, as shown in FIG. 2
The quick connector 18 is constructed such that O-rings are fitted in the inner cylindrical wall of the pipe inserting section 26 of the coupling body 24. This is to connect the metal pipe to coupling 18 in one action.
In this connection, it has been found that, if the electrical resistance of the coupling body 24 is in a predetermined range, then the current which expedites the deterioration of the coupling body 24 does not flow in the contact part of the coupling body 24 and the metal pipe 22. As a result, the following fuel hose resin coupling has been created.
The coupling mechanism 18 according to the present invention has an O-ring 28 fitted in the inner cylindrical wall of the pipe inserting section 26 of the coupling body 24. A specific feature of the coupling mechanism 18 is that the volume resistivity of the coupling body 24 is within a range of 106 to 1010 xcexa9xc2x7cm and the surface resistivity is within a range of 106 to 1010 xcexa9.
In this connection, it is preferable that the coupling body 24 has an electrically conductive film 30, because the surface resistivity of the coupling body 24 can be readily set in the above-described range.
In addition, it is preferable that an electrically conductive elastic member 32 is arranged on the bottomed step 27 of the pipe inserting section 26. In this embodiement, it is preferable that each of the volume and surface resistivities of the elastic member 32 is smaller than those of the coupling body 24, because the discharge path is well maintained.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.